The developmental loss of cerebellar Purkinje cells that occurs in autism spectrum disorders has been associated with a heterogeneous pattern of cognitive deficits that cannot be explained by a unitary cognitive impairment. It is very unlikely that the simple loss of cerebellar Purkinje cells can directly account for these myriad cognitive deficits. Rather, it is likely that autism is, at its essence, a disconnection syndrome that results, at least in part, from a disruption of cerebellar modulation of the prefrontal cortex (PFC). We have exciting new data suggesting that the cerebellum modulates PFC dopamine levels. Here we propose to investigate the disconnection hypothesis that cerebellar pathology results in dopaminergic abnormalities in the prefrontal cortex (PFC) and underlies some of the core neuropsychiatric symptomatology of autism. In Aim 1 we will determine the pathway(s) whereby the cerebellum modulates dopamine release in the PFC and glutamate release in subnuclei comprising the cerebellum to PFC pathways and the neurochemical, electrophysiological, anatomical, and behavioral consequences of a disconnection between these two structures. Aim 1 will compare wildtype (control) and Lurcher mice that loose all Purkinje cells, to determine the consequences of complete loss of Purkinje cells on cerebellar-PFC communication. Aim 2 will investigate the behavioral and physiological consequences of partial loss of Purkinje cells - as typically found in autistic brains. Using Lurcher-wildtype chimeras with varying developmental loss in Purkinje cell numbers we will determine how neurochemical, electrophysiological, anatomical and behavioral indicators of PFC function depend on Purkinje cell number. Given the well documented reductions in cerebellar neuron number that are found in autism spectrum disorders, the neurochemical, electrophysiological, anatomical and behavioral analyses of chimeric mice presents a unique opportunity to model both the developmental and cerebellar aspects of these syndromes.